Enhances MQTT server logging

Improves logging for MQTT server events to provide more detailed
information for debugging and monitoring. Logs the message payload
when a client publishes a message and includes username, password,
and remote IP address when an observer fails to connect due to
invalid credentials.

Source/ProofOfConcept/Services/MQTTServer.cs

@@ -1,4 +1,5 @@
 using System.Net;
+using System.Text;
 using Microsoft.Extensions.Options;
 using MQTTnet.Protocol;
 using MQTTnet.Server;
@@ -54,7 +55,7 @@ public class MQTTServer : IHostedService
                 return Task.CompletedTask;
             }
 
-            logger.LogInformation("Client {ClientID} published message to topic: {Topic}", e.ClientId, e.ApplicationMessage.Topic);
+            logger.LogInformation("Client {ClientID} published message to topic: {Topic}: {Message}", e.ClientId, e.ApplicationMessage.Topic, Encoding.UTF8.GetString(e.ApplicationMessage.Payload));
             return Task.CompletedTask;
         };
 
@@ -93,7 +94,7 @@ public class MQTTServer : IHostedService
             {
                 if (e.UserName != configuration.Observer.Username || e.Password != configuration.Observer.Password)
                 {
-                    logger.LogWarning("Observer tried to connect with invalid credentials");
+                    logger.LogWarning("Observer tried to connect with invalid credentials: {Username} / {Password} from {RemoteIP}", e.UserName, e.Password, e.RemoteEndPoint is IPEndPoint ipEndPoint ? ipEndPoint.ToString() : e.RemoteEndPoint.GetType().FullName);
                     e.ReasonCode = MqttConnectReasonCode.NotAuthorized;
                 }
             }